1. Field of the Invention
The invention relates generally to efficient means for the generation of electrical power utilizing energy from geothermal sources and, more particularly, relates to arrangements for suspending and sealing in operating relation hot geothermal water pumping equipment in deep, hot water wells for the transfer of thermal energy to the earth's surface.
2. Description of the Prior Art
A prior art advance in the art of extraction and use of geothermal energy is reflected in the H. B. Matthews U.S. Pat. No. 3,824,793 for a "Geothermal Energy System and Method," issued July 23, 1974 and assigned to Sperry Rand Corporation. This prior Matthews invention provides means for efficient power generation employing energy derived from geothermal sources through the generation of dry, super-heated steam and the consequent operation of sub-surface equipment for pumping extremely hot well water at high pressure upward to the earth's surface. Clean water is injected at a surface station into the deep well where thermal energy stored in hot solute-bearing deep well water is used at a deep well station to generate super-heated steam from the clean water. The resultant dry, super-heated steam is used at the well bottom for operating a turbine-driven pump for pumping the hot solute-bearing well water to the earth's surface, the water being pumped at all times in the system at a pressure sufficient to prevent flash steam formation. The highly energetic water is used at the surface power station in a binary fluid system so that its thermal energy is transferred to a closed-loop surface-located vapor generator-turbine system for driving an electrical power alternator. Cooled, clean water is regenerated by the surface system for re-injection into the well for operation of the steam turbine therein. Undesired solutes are pumped back into the earth via a separate well in the form of a concentrated brine.
In the H. B. Matthews U.S. Pat. No. 3,967,448 for a "Geothermal Well Casing Seal," issued July 6, 1976 and also assigned to Sperry Rand Corporation, there is described an improvement facilitating ready installation and reliable operation of such geothermal systems; according to that invention, there are provided means for the support of the deep well geothermal pump system within the well casing from the earth's surface by the pump-driven turbine exhaust steam conduit. In view of the differential expansion effects on the relative lengths of the casing extending downward from the earth's surface and the exhaust steam conduit contained therein, a particular flexible seal arrangement was provided between the suspended geothermal pump system and the well pipe casing. A first element of the improvement provided a vertical, smooth cylindrical sealing surface at the desired location for the deep well apparatus by means itself previously sealed to the well casing pipe. A second element assured easy assembly of a second seal interfacing the cylindrical sealing surface and suspended from the hot water pump so as to permit sliding motion of the seal in the prevailing hostile environment.
It is necessary to provide an efficient seal of some kind between the brine pump and the well casing; otherwise, a differential pressure would never be built up across the brine pump impeller. While the seal of the prior Matthews patent has certain established advantages for this purpose, it is complex and expensive. This expensive design will seal against very high differential pressures and is effectively leak-proof, while some leakage may actually be permitted. The packer used in the prior arrangement requires a large-diameter casing, whereas casings of more conventional dimensions are less expensive and evidently preferred. The prior art fixed packer is relatively expensive to buy and to insert, adding considerably to the time required for deployment of the equipment in the geothermal well. The fixed packer must be drilled out when it is to be removed.